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brokenrinker

current leakage

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I'm working  on a '35 Chrysler  Airflow. I've  switched  it to 12volt  and installed a GM 3 wire alternator. I noticed  that when I measure resistance  across the disconnected  battery terminals  I get about 6000 ohms. I disconnected  everything  but the alternator. When I pull the two wire plug out of the side of the alternator  the resistance  across the battery  terminals increases  to the Meg ohm range but doesn't  drop to zero.

Any thoughts?

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I would recheck the wiring to make sure everything is correctly connected.  Certainly there has to be a path from the battery to the alternator for the battery to charge.  A 6k ohm resistor connected to 12v produces a current flow of 0.002A.  

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The alternator circuit has a diode between the ignition  switch and one of the terminals  on the alternator. Evidently  it's  there to prevent the engine  from continuing  to run even after the key had been turned off. Could that have something  to do with it?

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So just out of curiosity, are you troubleshooting a problem relating to the charging system or creating one where one doesn't exist?

 

Seriously, take a look at the attached wiring diagram. If you are measuring resistance between the disconnected + battery cable and the battery terminal, note that there is a direct path to ground through the resistors in the regulator (R2 and R3).

SI wiring.png

Edited by joe_padavano (see edit history)
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I'm  glad you're  curious.  I was creating  a problem  where none existed. Your  schematic  explains it. Everything  works fine, charging  etc. I have done a ton of wiring  work and I happen to be standing next to the battery  cables holding a multimeter. I checked resistance  across the two leads  expecting to see an open circuit. When I saw some resistance   (current flow) I got confused, which is a common occurrence  with me. Thanks!

Edited by brokenrinker (see edit history)
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Just for education, zero ohms is a circuit with no resistance, or a perfect conductor. Megohms is approaching infinity ohms. So an open circuit is described as infinite ohms, not zero ohms. Drop to zero means no resistance, a "short", not an open circuit.

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7 hours ago, joe_padavano said:

So just out of curiosity, are you troubleshooting a problem relating to the charging system or creating one where one doesn't exist?

 

Seriously, take a look at the attached wiring diagram. If you are measuring resistance between the disconnected + battery cable and the battery terminal, note that there is a direct path to ground through the resistors in the regulator (R@ and R3).

SI wiring.png

 

Is that schematic for the 10si/12si?

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Hi Broken

 

You have now joined the exclusive club for those of us that have to much technical experience and way to much time on our hands........

 

Also, Thanks Joe.  That schematic will be very helpful to those of us that want to find the real answer for GM alternator failures ;) .

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10 hours ago, 37_Roadmaster_C said:

Also, Thanks Joe.  That schematic will be very helpful to those of us that want to find the real answer for GM alternator failures ;) .

 

In that case, you might find this Service Bulletin from Delco Remy useful. Yes, it only covers 10SI, 15SI, and 27SI, but the 12SI is essentially the same as the 10SI.

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The easiest way to check for a battery drain is to take the ground terminal off the battery and connect a test light between the battery post and the terminal. The light should not even glow a barely visible dim red color. To check if you have it connected correctly and that the test light is good open the door or turn something on, the set light will glow brightly. This can even be used on new cars with computers but there are other steps you must follow. If the light is glowing and everything is off disconnect one thing at a time until the bulb goes out.

Best of luck

 

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